It is well known to use a compaction machine having a compaction drum in leveling a road surface in the road construction industry. Furthermore, it is also well known that better results and better efficiency are achieved by causing small high-frequency vibrations in the compaction drum during such leveling. Vibrations are often generated by rotating an eccentric weight within the compaction drum. Moreover, the amplitude of vibration is dependent upon the rotational rate of the eccentric weight; however, the amplitude of vibration is also dependent upon the radial spacing of the center of mass of the weight to the axis of rotation, i.e., the eccentricity of the weight.
In Schmelzer et al. U.S. Pat. No. 4,830,534 (the '534 Patent), vibrations in the compaction drum are generated by rotation of an eccentric weight mounted on a rotor shaft. A high amplitude of vibration or, alternatively, a low amplitude of vibration is produced depending upon the radial position of the eccentric weight with regard to the axis of rotation of the shaft. Springs are provided in the mounting of the eccentric weight and, when the eccentric weight is not undergoing rotation, the springs urge the eccentric weight into a default radial position in abutment with the shaft. A latch fixedly mounted to the shaft controls the radial positioning of the eccentric weight as well as drives the rotation of the eccentric weight. In particular, the latch includes a slot and the eccentric weight, which is rotatably mounted on the shaft, includes a pin that extends axially through the slot. Rotation of the latch in a first direction causes the pin to move to a first end of the slot which, in turn, moves the weight into a low radial position with respect to the axis of rotation, thereby generating a low amplitude of vibration. Furthermore, the slot is C-shaped or L-shaped and a side of the slot engages the pin and thereby restrains the weight from moving into a higher radial position. Rotation of the latch in the reverse direction causes the pin to move to the other end of the slot and causes the eccentric weight to move into a high radial position, thereby generating a high amplitude of vibration.
An object of the present invention is to provide a vibration generator for a compaction machine which exhibits both high and low amplitude of vibration states without utilizing the vibration generator of the '534 Patent.